1. Field of the Invention
The invention relates to a chambered doctor blade assembly which can be placed against a roller of an inking unit of a printing machine, the assembly including a chamber having an orifice through which ink is introduced to the roller.
2. Description of the Related Art
In anilox printing units, chambered doctor blade assemblies are often used in planographic and flexographic printing in order to ink anilox rollers. The designation xe2x80x9cengraved rollersxe2x80x9d is also customary for anilox rollers, since cells capable of being filled with ink are arranged in the form of a grid in their surface. DE 298 05 201 U1 discloses a chambered doctor blade assembly which is placed against an engraved roller of a rotary offset printing machine and which is connected to an ink duct. The printing ink from the ink duct is pumped with the aid of an ink pump to a chamber of the chambered doctor blade assembly, the chamber being connected to the surface of the engraved roller by means of an orifice, in order to flush and fill the cells of the engraved roller.
In the case of a change of ink, however, there is the problem that all the parts which have come into contact with ink have to be cleaned, that is to say, for example, also return ducts and connecting hoses. This is highly complicated, above all in the case of planographic machines. Since the ink dries on the parts of the chambered doctor blade assembly, the parts which have come into contact with ink have to be de-mounted and cleaned. The new ink must subsequently be pumped into the then clean chambered doctor blade assembly, which takes up a certain amount of time.
By contrast, the object on which the present invention is based is to provide a chambered doctor blade assembly of the type mentioned in the introduction, by means of which a rapid change of ink is possible.
This object is achieved, according to the invention, by means of a closing element merged in the chamber and movable between a closing position, in which ink can flow through the orifice onto the roller, and a closing position, in which the orifice is closed and ink can still circulate through the chamber.
When the chambered doctor blade assembly according to the invention is removed from the impression roller on the occasion of a change of ink, complicated cleaning may be dispensed with, because the chamber is closed in an ink-tight and air-tight manner by the closing element and the printing ink, still located in the chamber, is therefore not exposed to any drying or oxidation processes. The chambered doctor blade assembly, together with the stored printing ink, consequently remains storable in this state until further use and can be re-used without further cleaning or refilling work. As a result, on the one hand, time is saved and, on the other hand, less cleaned-off ink has to be disposed of.
Furthermore, even with the orifice closed, that is to say without ink being applied to the impression roller, printing ink is capable of flowing through the chamber. Consequently, printing ink can continue to be circulated within a closed ink circuit. This is advantageous, particularly before the start of printing, in order to lower the viscosity of the ink, due to its thixotropy, at this early stage to a level which would otherwise occur only later during printing operations. The circulation of printing ink can take place even without the chambered doctor blade assembly being placed against the impression roller, with the result that the wear of the roller and of the doctor blades are reduced.
According to preferred embodiments, the chambered doctor blade assembly is releasably connected to ink-supplying lines and to ink-discharging lines by means of selfclosing couplings. The chambered doctor blade assembly can thereby be uncoupled from the ink circuit, without the ink located in the chamber drying out or coming into contact with oxygen.
According to a development of the invention, in the closing position, sealing surfaces of the closing element can be brought to bear on matching sealing surfaces of a chambered doctor blade assembly housing, at least one of the sealing surfaces being provided with a soft coating. Consequently, elastic adaptation of the sealing surfaces to one another can take place, with the result that the sealing effect is improved.
According to a preferred embodiment, the closing element is formed by a strip which extends parallel to the roller axis and which is capable of being moved back and forth radially with respect to the roller between bearing contact on a bottom-side abutment in the chambered doctor blade assembly housing (opening position) and bearing contact on the sealing surfaces of the chambered doctor blade assembly housing (closing position). In the closing position, a bypass conduit for the ink flow is then present between the bottom-side housing abutment and a bottom surface of the strip. The pressure force acting on the bottom surface of the strip and originating from the ink pressure within the ink circuit consequently advantageously assists the bearing contact of the strip on the sealing surfaces and ensures an improved sealing effect.
According to a further embodiment, the closing element is formed by a tube which extends parallel to the roller axis and is rotatably mounted within the chamber. A circularly arcuate closing body on the outer surface of the tube is integrally formed. In angular opening position, this body faces away from the engraved roller. In order to close the orifice, the closing body can be rotated into the latter tangentially into an angular closing position in which it is located opposite the engraved roller. In this case, the inflow of printing ink takes place through the tube interior, a tube wall of the tube being provided with at least one passage bore which is arranged downstream of the closing body, as seen in the direction of flow of the ink. This bore precedes the orifice in the angular opening position, in order to supply printing ink to the orifice, and follows the orifice in the angular closing position, in order to discharge the printing ink via a return-flow conduit in the bottom of the chambered doctor blade assembly housing. The flow cross section of the tube, in this case, is large as compared with that of the passage bore. By virtue of this measure, the ink is first distributed along the longitudinal extent of the tube running parallel to the roller, before it is transferred through the orifice onto the roller, thus bringing about a uniform distribution of the ink over the length of the roller.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.